feat: ensure thinking blocks are present for tool use and enable reasoning content in DeepSeek presets

[linw1995]

No description provided.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 91.79104% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 51.79%. Comparing base (e5977ab) to head (62d5230).
⚠️ Report is 8 commits behind head on dev.

Files with missing lines	Patch %	Lines
src/agent.rs	90.47%	10 Missing ⚠️
src/provider/openai.rs	93.75%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #105      +/-   ##
==========================================
- Coverage   53.46%   51.79%   -1.67%     
==========================================
  Files          88       91       +3     
  Lines       21248    23428    +2180     
==========================================
+ Hits        11360    12135     +775     
- Misses       9888    11293    +1405     

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